Bypass heart pump and oxygenator system



BYPASS HEART PUMP AND OXYGENATOR SYSTEM,

Filed Sept. 15. 1966 y 26, .3 M. G. CHESNUT ET AL GSheets-Sheet 1SIM/75' L EVEE MANUAL PUMP OXYGEA/HTOR l VENOUS Esra/e VENOUS PssEEvo/EMay 26, 1970 G. CHESNUT ETAL 3,513,845

BYPASS HEART PUMP AND OXYGENATOR SYSTEM Filed Sept. 15, 1966 eSheets-Sheet 2 r v F .Lfl

1 1 w HP 4 4Q N i T T :B 47' A FV LV l L c I V r 15! J0 10' v I c P 2 P"7 92'- ,54 Q"- v Br F jfi'l! 1 12 w W N 1 L L May 26, 1970 M. CHESNUTETAL BYPASS HEART PUMP AND OXYGENATOR SYSTEM Filed Sept. 15, 1966 6Sheets-Sheet 5 May 26, 1970 M. s. CHES NUT ET AL 3,5 4

BYPASS HEART PUMP AND OXYGENATOR SYSTEM Filed Sept. 15, 1966 6Sheets-Sheet;

6 Shets-Sheet 6 May 26, 1970 M. G. CHESNUT ET AL BYPASS HEART PUMP ANDOXYGENATOR SYSTEM Filed Sept. 15, 1966 United States Patent 3,513,845BYPASS HEART PUMP AND OXYGENATOR SYSTEM Merrill G. Chesnut, Arvatla,Phillip B. Callaghan, Westminster, and Sven Gafvert, Boulder, Colo.,assignors, by

mesne assignments, to United Aircraft Corporation, a

corporation of Delaware Filed Sept. 15, 1966, Ser. No. 579,565 Int. Cl.A61m 1/03 U.S. Cl. 128214 5 Claims ABSTRACT OF THE DISCLOSURE Acardiopulmonary bypass includes a reciprocating pump to deliver bloodfrom a reservoir fed by an oxygenator to the femoral arteries. Theoxygenator receives blood from either a venous roller pump or areciprocable pump which draws the blood from a venous reservoir that inturn is fed by catheters placed into the superior and inferior venacavae. The pumps are controlled by computer circuitry which provides therate, the volume and the speed of blood flow under various controls. Thesystem includes controls to permit utilization of an arterio-arterialassist device rather than as a complete cardiopulmonary bypass device.This includes the elimination of a check valve by utilizing difierentialflow crosssections. In one embodiment, a second roller pump deliversblood from a reservoir of the oxygenator to a bubble trap, the output ofwhich is returned to the patient through a reciprocating pump.

This invention relates generally to heart pump systems for replacing thefunction of a patients heart, and more particularly to a heart pumpingsystem for complete cardiopulmonary bypass.

In complete or total cardiopulmonary bypass, the total blood flow fromthe venous side of the patients circulatory system is withdrawn,oxygenated, and returned to the arterial side of the system undersuflicient pressure to perfuse the peripheral arterial tree. In systemsof this type, in contradistinction to partial veno-arterial bypass,bypass of the right heart, and bypass of the left heart, the entireoxygenating function is effected by an extra corporeal oxygenator ratherthan the patients lungs.

A primary limitation in prior known cardiopulmonary bypass systems isthat they have not had long-term capabilities due to the development ofmetabolic acidosis after extended perfusions. Metabolic acidosis may bedefined as the acid products released in the circulatory systemresulting from a lack of oxygen in the blood causing the incompletecombustion of carbohydrates, fats and proteins. The tissue hypoxiaresulting from metabolic acidosis is most prevalent in the use of steadystate heart pump systems, such as those employing roller pumps, but alsoappears to result from the use of known pulsatile systems.

The peripheral pooling of blood during long perfusions with resultinghypoxia has been relieved somewhat using presently known techniques ofhemodilution. Further, operative respiration of the lungs with heliumand drainage of the left ventricle during bypass have obviated some ofthe alveolar collapse and interstitial hemorrhage encountered with priorknown systems and techniques. However, from the circulation standpointthe high rates of flow necessary in these prior systems have producedexcessive damage to the blood and overloading of the reticluoendothelialsystem, plugging of the renal tubules and acute renal failure. In priorsystems these high rates of flow have been necessary because low flowrates lead to the development of metabolic 3,513,845 Patented May 26,1970 ice acidosis, often times during fairly short time intervals ofperfusion. However, as the length of perfusion has increased, three hasbeen found to develop a paradoxical metabolic acidosis even when theperfusion rate matches the normal cardiac output. Many authors explainthis development as due to a sl-udging of the blood in the peripheralarterial tree.

Attempts have been made by various investigators to avoid the metabolicacidosis by lowering the oxygen requirement of the tissues byhypothermia. However, hypothermia produces its own problems, e.g., atten degrees centigrade (despite the great reduction in oxygenrequirement) the temperature of the blood limits circulation profoundly.

It is therefore a primary object of the present invention to provide anew and improved total cardiopulmonary bypass system in whichmicrocircultaion is better perfused without employing flow rate rateshigh enough to rupture coronary vessels, thus enabling the system tomaintain artificial circulation for longer periods of time andpermitting more complicated surgical procedures to be attempted on thepatient.

A further object of the present invention is to provide a new andimproved pulsatile cardiopulmonary bypass system which in general willeliminate the patients tendency toward metabolic acidosis even overlong-term perfusions.

A further object of the present invention is to provide a new andimproved pulsatile cardiopulmonary bypass system of the type describedin which the arterial flow rate may be controlled by the surgeon asdesired by simultaneously varying the speed and stroke length of apulsatile pump in the system.

A more specific object of the present invention is to provide a new andimproved bypass system of the type described above in which triggeringsignals from a variable rate pacemaker initiate each cycle of thepulsatile pump, and an automatic computer circuitry maintainscoincidence between each pumping cycle and the period of the triggeringsignals and also varies the flow rate by automatically varying the speedof stroking of the pump in response to changes in the selected volume bythe surgeon.

Another object of the present invention is to provide a new and improvedcardiopulmonary bypass system of the type described above in which aroller pump is provided for withdrawing blood from the venous side ofthe patients circulatory system and delivering it to an oxygenator, andincluding a reservoir for receiving blood from the oxygenator prior toentry into a blood pumping chamber in the pulsatile pump.

A still further object of the present invention is to provide animproved cardiopulmonary bypass system, somewhat modified from thatdescribed immediately above, in which two roller pumps are provided, onefor pumping blood into the oxygenator and the other for withdrawingblood from the oxygenator and delivering it to the blood pumping chamberin the pulsatile pump.

Another object of the present invention is to provide a cardiopulmonarybypass system of the type described generally above, but in somewhatmodified form in that a second pusatile pump is provided for withdrawingblood from the venous side of the system and delivering it through theoxygenator in place of the roller pumps, thereby more nearly simulatingthe physiological function of the human heart.

Still another object of the present invention is to provide a heartpumping system which may be used as a complete cardiopulmonary bypassduring an operation and as a circulation assist postoperatively.

In accordance with the present invention, a reciprocating pistonpulsatile pump is provided in which each pumping cycle is initiated bytriggering signals from a pacemaker in the form of an oscillator in anassociated con trol circuit. A pumping cycle as defined herein is onecomplete reciprocation of the pumping piston Within the pulsatile pump,i.e., a push and a withdraw stroke. The reciproeating piston defines anexpanding and contracting fluid chamber within the pump connected toreceive oxygenated blood and deliver it in pulsatile fashion to thearterial side of the patients circulatory system. Several means aredisclosed for withdrawing the blood from the patients vena cavae,oxygenating the venous blood, and delivering it to the blood pumpingchamber in the pulsatile pump.

While each pumping cycle is initiated by the pump triggering signalreferred to above, a computerized control circuit is provided forvarying the time base of each pumping cycle so that it coincides withthe period of the triggering signal by normally maintaining the lengthof stroke selected by the surgeon and varying the rate of travel of thepumping piston to achieve this coincidence. However in completecardiopulmonary bypass, as there is no essential relationship betweenpulsatile flow initiation and the patients natural heart action, thepacemaker may be adjusted by the surgeon to the desired rate. Thepresent computer circuitry does permit the surgeon to select the desiredrate and volume and the computer circuitry automatically initiallycomputes the proper pumping or stroke speed to eliminate dwell oroverlap between the pumping cycles.

The regulation of arterial flow rate, which is one of the importantaspects of the present invention, is effected in the presentcomputerized control by the rate and volume control circuitry. Thevolume circuitry permits the surgeon to merely select the desired volumeof blood to be pumped per cycle and the system automatically computesthe correct pump speed and stroke length to achieve the selected volumewithout varying the time base for the pumping cycle dictated by therepetition rate of the triggering signal described above. It is thisinterrelationship between pumping speed, stroke length and cycle timethat provides the capability of the present device of longtermperfusions and the elimination of metabolic acidosis produced by priorknown systems.

The present system when used in complete bypass fashion providesadequate blood pressure profiles with low blood flow rates. These lowflow rates are sufiicient to avoid metabolic acidosis but are low enoughnot to rupture the coronary arteries.

Other objects and advantages will be readily apparent from the followingdetailed description taken in connection with the accompanying drawingsin which:

FIG. 1 is a diagrammatic view of the present bypass system shown withits connections into the patients circulatory system;

FIG. 2 is a sub-assembly view of a portion of the pump shown in FIG. 1;

FIG. 3 is a simplified diagrammatic view of the system shown in FIG. 1;

FIG. 4 is a diagrammatic view of a system similar to that in FIG. 1employing two roller pumps in addition to a pressure pulse generator;

FIG. 5 is a diagrammatic view of a somewhat modified system employingtwo reciprocating piston pumps;

FIG. 6 is a schematic diagram of a portion of the con trol circuitincluding the pacemaker input circuitry and the reciprocating pump servocoils;

FIG. 7 is a schematic diagram of another portion of the controlcircuitry including a digital counter;

FIG. 8 is a schematic diagram of the computer portion of the controlcircuit which selects the volume, push and withdraw rates, and cycletime of the reciprocating pump of FIG. 1;

FIG. 9 is a schematic diagram of timing error sensors which determinethe error in the pump g cycle m FIG. 10 is a schematic diagram of areduced augmentation circuit which selects only certain heartbeats toinitiate the pumping cycles; and

FIG. 11 is a partial schematic diagram of the power supply for thecontrol circuits.

While this invention is susceptible of embodiment in many difierentforms, there is shown in the drawings and will herein be described indetail embodiments of the in vention with the understanding that thepresent disclosure is to be considered as an exemplification of theprinciples of the invention and is not intended to limit the inventionto the embodiments illustrated. The scope of the invention will bepointed out in the appended claims.

Referring to the system shown in FIG. 1 of the drawings, a pressurepulse generator 10 is provided generally similar to the pump shown inour copending application, Ser. No. 406,722 filed Oct. 27, 1964,assigned to the assignee of the present invention. Reference should bemade to this application for a more detailed description of the pump 10.It will only briefly be described herein with particular reference to acombined on and off check valve 11 shown in FIG. 2 which permits bothcomplete bypass operation and arterio-aiterial circulation assist.

The pump 10 includes a multi-member housing 13 having a cylinder formedtherein which slidably receives a reciprocating piston 15 defining inthe housing 13 a pumping chamber 16 and an actuating chamber 17.

A controller 20 described in more detail below delivers fluid in twodirections through the fluid coupling 22 to the actuating chamber 17thereby reciprocating the piston 15 in forward and reverse strokes,sometimes referred to herein as push and withdraw phases, respectively.

As shown in FIGS. 1 and 3, the pump 10 is connected in completecardiopulmonary bypass so that blood flow from the heart and through thelungs is terminated and circulation and oxygenation is eifectedextracorporeally by the artificial system. Toward this end venous bloodis drained by catheter assembly 27 from the superior and inferior venacavae which normally drain into the right atrim 25. This blood isdrained by gravity into a venous collecting chamber 28. The chamber 28should be placed below the level of the operating table for this gravityfeed.

Venous blood in the reservoir 28 is pumped by a roller pump 30 throughan oxygenator 32. The roller pump 30 may be any one of a number ofcommercially available units of this type. The oxygenator 32 may takeseveral forms including the bubble type, disc, screen, or even membranetype.

Blood in the oxygenator drains by gravity into a reservoir 36. No bubbletrap is required in this embodiment as any bubbles in the blood willrise to the top of the reservoir.

The reservoir 36 is connected to fitting 40 shown in FIG. 2communicating through check valve 11 with the pumping chamber 16in thepump 10.

The valve 11 may be manually operated to either block flow from thereservoir 36 into the chamber 16, or to permit flow from the reservoirbut prevent back flow from the chamber 16 into the reservoir. For thispurpose a manually rotatable valve member 42 is provided with a largediameter through passage 43 therein. When valve member 42 is rotated sothat passage 43 is aligned with bore 44 in the fitting, fluid may flowfrom the reservoir 36 into the chamber 16. This is the valve openposition, and is so placed when the system is used in complete bypass.During postoperative circulation assist the valve 42 may be rotateddegrees from its valve open position closing bore 44. The function ofthis is described in more detail below.

A check valve assembly 47 is mounted within a passage 43 and permitsflow from the reservoir 36 into the chamber 16, but prevents flow fromthe chamber into the reservoir. In this manner during the push stroke ofthe piston 15 blood will flow from chamber 16 into the patients arterialsystem rather than back into the reservoir 36.

The pumping chamber 16 is connected into the circulatory system througha catheter assembly 49 connected to fitting 50 (FIG. 2). The catheterassembly may be similar to that shown in our copending application,which in cludes branched catheters adapted for insertion into thefemoral arteries up into the patients descending aorta.

It should be noted that there are no check valves in the catheterassembly 49 preventing flow from the arterial side of the patientscirculatory system into the pumping chamber 16 as the piston 15withdraws. To prevent any significant amount of blood from being removedfrom the arterial tree during this withdrawal action, the diameters ofthe bore 44 and passage 43 are large compared with the smallest diameterof the catheter assembly 49 so that the catheters offer much greaterresistance to flow during the withdrawal of piston 15 than the passagesconnected with the reservoir 36.

As the piston 15 moves in its push phase forcing blood into the arterialtree, the check valve 47 prevents reverse flow into the reservoir 36.

As the controller and actuator 20 delivers fluid through the coupling22, piston 15 reciprocates drawing blood into chamber 16 through checkvalve 47 (with valve member 42 open), and in the opposite phase forcingblood from the chamber 16 through catheter assembly 49 into the arterialtree. This action provides pulsatile perfusion of the blood in thearterial tree.

In FIG. 4 a cardiopulmonary bypass system is shown generally similar tothat shown in FIGS. 1 to 3 except that the reservoir 36 is replaced by acombination of a second roller pump 52 and a bubble trap 54. With thisarrangement blood is forced into the pumping chamber 16' rather thanbeing fed by gravity from a reservoir such as noted with respect toFIGS. 1 to 3. When piston 15' withdraws during the withdrawal phase,both the pressure from roller pump 52 and the Withdrawal action of thepiston 15 cooperate in filling the chamber 16'. There is only minimalleakage through the valve 47' during the push phase of the pump 10' asthe pressure in chamber 16' is above the output pressure from pump 52,although the valve 47 closes somewhat slower in this embodiment than inthe embodiment of FIGS. 1 to 3.

Since the system shown in FIG. 4 is essentially closed from theoxygenator to the arterial side of the patients circulatory system, thebubble trap 54 is required to removed gases entrained in the blood.

The minute flow in the system shown in FIG. 4 is somewhat higher thanthat shown in FIG. 3 due to the additional filling assist of chamber 16'by the pump 52.

In the FIG. 5 embodiment, a cardiopulmonary bypass system is disclosedgenerally similar to those described above with reference to FIGS. 1 to4 except that an additional pulsatile pump 56 is provided forWithdrawing blood through valve 58 from the reservoir 28". Valve 58 is acheck valve and may be similar in construction and operation to thevalve 11 shown in FIG. 2. Pump 56 during its withdraw phase draws fluidfrom reservoir 28", and during its push phase pumps blood intooxygenator 32.". The withdrawal of blood from the oxygenator 32" iseffected by the withdrawal action of piston 15" in pump A bubble trap54' is also necessary as the system is a closed one from the oxygenator32". Suitable circuitry is provided (not shown) to balance the output ofthe pumps 56 and 10" so that they may operate under diflerent loadsituations preventing the oxygenator 32" from being either flooded withtoo much blood or being drained dry.

In all the above systems the intermittent infusion of blood into thearterial tree produces a pulsatile arterial pressure wave. The height oramplitude of this wave may be increased by increasing the travel of thepiston and for this purpose a suitable volume dial is provided on thecontroller in FIG. 1 which permits the surgeon to select the desiredvolume per cycle of the pump. In addition, the relative time duration ofthe positive pressure wave in comparison to the total cycle time of thepump may be altered by changing the relative time duration of the pushand withdraw phases of the piston 15. Furthermore, the length of cycleis also governed from the controller 20 by changing the rate ofpacemaker which provides triggering signals for each cycle of the pump.During complete cardiopulmonary bypass the phase relationships betweenthe patients natural heart action and the synthesized wave produced bythe pump 10, important in assisted circulation, are of no importance.

The control circuitry described below, contained in the controller 20,exercises control over the pumping parameters of stroke length, speed ofstroking during both push and withdraw phases, and pump cycle duration.It should be understood at this point that only portions of thedescribed circuitry are operative during complete cardiopulmonarybpyass, the other portions being operative during arterio-arterialassist as a postoperative circulation aid.

Triggering and driving circuit The triggering and driving circuitdisclosed in FIG. 6 is generally adapted to develop triggering signalsfor initiating each cycle of the reciprocating pump 10. For completecardiopulmonary bypass, a pacemaker 132, which may take the form of anastable multivibrator, provides triggering pulses for the pumpingcycles. A suitable control 132a is provided for varying the repetitionrate of the triggering signals from the pacemaker so that the surgeonmay select the cyclical rate he desires. For arterio-arterial assist,which is employed as a postoperative measure in the present device, anEKG trigger level selector is provided for initiating the pumping cyclesin timed relationship with the patients EKG waveform. It should beunderstood that the pacemaker 132 and the trigger level selector 125 areused selectively.

In the arterio-arterial mode, the triggering circuit is effective todevelop triggering pulses and delay them from a selected trigger levelportion of the QRS segment of the EKG wave at a predetermined triggerlevel, and derives and delays a triggering pulse therefrom. Thetriggering pulse derived initiates the push phase of the pumping cycleand effects delivery of fluid into the patients aorta increasingintra-aorta pressure at a time when the workload of the heart is thelowest. As noted above, during postoperative arterio-arterial assist thevalve 11 would be closed. The delay time for the triggering pulsedetermines the phase relationship of the pumping cycle to the arterialpulse wave, and is determined physiologically as the phase relationship,which reduces the intraventricular pressure to a minimum for a givenvolume pumped and increases the postsystolic arterial pressure to anextent which returns the intra-aortic pressure to its pre-pump level orbetter so that coronary and peripheral circulation may be assisted. Thewithdrawal phase begins immediately upon completion of the pumping phaseand continues during aortic valve opening thereby aspirating the leftventricle into the aorta. The withdrawal phase continues until the peakof the next intraventricular waveform at which time another pumping orpush phase begins in response to another triggering signal. This phaserelationship is not of any significance in the complete cardiopulmonarybypass as there is no load on the patients heart.

As shown in FIG. 6, an EKG trigger level selector 125 is connected toreceive the patients EKG waveform from a conventional electrocardiogramthrough line 126. Line 126 connected to line 127 is adapted to drive anoscilloscope so that the patients EKG waveform may be viewed during theuse of the heart pumping system in the arterio-arterial mode by thesurgeon or technician. Reference should be made to the copendingapplication Chesnut et al. for the details of construction of thetrigger level selector 125.

A selector switch 131, which may be located on a convenient controlpanel, permits the alternate initiation of 7 the pumping cycles by thepacemaker 132, by the EKG trigger level selector 125, or by the manualstroke initiate switch 133. As noted above, during completecardiopulmonary bypass, with which the present invention is mainlyconcerned, the switch 131 is placed in its uppermost position connectingthe pacemager 132 to a trigger delay circuit 136 through line 135. Withswitch 131 in its central or middle position, it connects the triggerlevel selector 125 to the trigger delay circuit 136 through line 135.And when switch 131 is in its lowermost position, the manual position,the upper half of switch 131 is ineffective but the lower half of theswitch is connected to a power supply which places the pump cycle undermanual control.

The trigger delay circuit 136 delays the actual triggering pulse behindthe selected portion of the patients EKG waveform duringarterio-arterial assist. It may c nsist of a standard dual PNPtransistor one shot multivibrator with base triggering. Its RC timeconstant is manually adjustable with a potentiometer 138 which may bemounted on the control panel. The potentiometer 138 provides anadjustment of the delay time. The output triggering pulse from thetrigger delay circuit 136 triggers a refractory gate 140 which producesan 80 msec. pulse when triggered. The refractory gate 140 may be astandard dual PNP transistor one shot multivibrator with basetriggering. The delay provided by the delay circuit 136 is unnecessaryduring complete cardiopulmonary bypass.

The pulse from the refractory gate 140 comprises one of two inputs toAND gate 141. The AND gate 141 prevents any erroneous triggering signalfrom the refractory gate 140 from initiating the pumping cycle. If atriggering pulse from the refractory gate 140 is conducted to the ANDgate 141 prior to the receipt of a signal from the other input to theAND gate 141, i.e., line 143, which indicates a partial completion ofthe withdrawal stroke, the 80 msec. pulse will be held by the AND gatefor 80 msec. and if line 143 is not energized by that time, thetriggering pulse will be dropped. If a triggering pulse from therefractory gate 141 and a signal from line 143 are received by the ANDgate 141 simultaneously, blanking gate 144 passes a signal. The blankinggate 144 consists of a dual PNP transistor switch normally deactivatedby the lock-out gate 450. A signal in line 145 to the blanking gate 144blanks out selected triggering pulses in response to the reducedaugmentation circuitry described in more detail below. A pulse derivedfrom the blanking gate 144 is one of the two required enabling signalsto the AND gate 146. The AND gate 146 will not trigger the pumpingcycle, however, until a signal is received in line 151 which is theother input to the AND gate 146 indicating that the pump has completedits withdrawal stroke. This circuitry eliminates out-of-phase pumpingduring arterio-arterial assist by combining electronic control featureswith the physiological phenomenon known as the refractory period.

A pulse in line 150 from the AND gate 146 initiates the push phase ofthe pumping cycle by turning on a regenerative switch 148.

The regenerative switch 148 may consist of two transistor stagesconnected so that the output is fed back into the input. In addition,another NPN transistor switch shunts the first stage of the regenerativeswitch. A high voltage at the first stage turns on the regenerativeswitch, whereas the high voltage at the shunting NPN transistor turns itoff regeneratively. The presence of a high voltage in line 150 turns thefirst stage of the regenerative switch on and the second stage offthereby energizing line 151 and deenergizing line 152. Line 151energizes the pump servo coil 147 through the volume and rate computercircuitry shown in FIG. 8, while the energization of line 152 energizesthe withdrawal servo coil 154 through the same volume and rate computercircuit.

A pump phase signal, modulated by the volume and rate computer circuitrydescribed in more detail below with reference to FIG. 8, energizes linein FIG. 6 which drives the pump phase driver 161. The magnitude of thecurrent in line 160 determines the bias on the pump driver 163 andthereby the magnitude of excitation of the pump servo coil 147. The rateof travel of the piston 15 is directly proportional to the magnitude ofthe current in the pump coil 147 and the withdraw coil 154.

The servo coils 147 and 154 drive a servo valve (not shown) which portsfiuid to a reciprocating hydraulic actuator. The hydraulic actuatordrives fluid in two directions through coupling 22 shown in FIG. 1 whichin turn reciprocates the piston 15. Such a system is shown in our abovementioned copending application. Alternatively, the coils 147 and 154may be arranged to drive an electromagnetic actuator eliminating theneed for a hy- (lraulic servo valve and the associated hydrauliccircuitry. Connected to the actuator is a linear feedback potentiometer118 for indicating the actual position of the pumping piston 15.

As the piston 17 begins its push stroke driving the potentiometer 118, afeedback displacement signal from the potentiometer drives an invertingamplifier 170, the output of which is used to determine the errorbetween the actual pump and withdrawal displacement and the referencepump and withdrawal displacement signals determined by the computercircuitry shown in FIG. 8. Any error is fed back from the computercircuitry to line 172 in FIG. 6 whereby it is amplified by an ACamplifier 173 and integrated by a pump integrator 174 which excites apump error driver 177 for varying the bias on the pump driver 163.

An identical closed loop feedback circuit is provided as shown for thewithdrawal stroke and consists of line 189, AC amplifier 190, withdrawintegrator 191, a withdraw error driver 192, a withdraw phase driver188, and a withdraw driver 194. The error drivers are two-stage DCamplifiers which are collector coupled to the base of the NPN servodrivers for isolation purposes. The phase drivers 161 and 188 are PNPtransistors which are collector coupled in parallel with the errordrivers. The sevo drivers 163 and 194 may each be an NPN transistorwhich is connected in push-pull fashion to the associated servo coil.The servo drivers 163 and 194 are driven from an isolated source and arecollector coupled to the servo valve coils 147 and 154 for isolationpurposes.

As the feedback potentiometer 118 and the actuator shaft (connected withthe actuator described above) reach the end of the push stroke and asuitable mechanical stop (not shown), an end of pump stroke sensor 186provides a high voltage to the regenerative switch 148 to turn theswitch off, thereby energizing line 152 and deenergizing line 151. Theend of pump stroke sensor 186 may consist of an inverting PNP amplifierwhich drives the PNP comparator. The PNP amplifier emitter modulates thePNP comparator. The base of the comparator is biased by a potentiometeroffset amplifier 187. The output of the end stroke sensor 186immediately initiates the withdrawal stroke at the end of the pumpstroke. The potentiometer and the offset amplifier 187 which provides aVernier adjustment for the length of stroke may also be used to bias anend of withdrawal stroke sensor 200 to eliminate offset errors due tomechanical alignment tolerances between the piston 15 and the feedbackpotentiometer 118.

The energization of line 152 by the regenerative switch 148 enables thewithdrawal phase driver 188. The withdrawal rate errors are impressed inthe form of an error signal on line 189 and through the AC amplifier190, the withdrawal integrator 191 and the withdraw error driver 192providing a closed loop feedback on the withdrawal rate in the samemanner as the corresponding components in the pump error driver circuitdescribed above. A withdraw driver 194 energizes the withdraw servo coil154 to drive the pump piston 15 in its withdraw stroke thereby drawingblood from the reservoir 36 through valve 11 into the fluid chamber 16.

As the pump proceeds in its withdrawal stroke, the feedbackpotentiometer 118 is driven as shown in FIG. 6. An isolated oscilloscopejack 197 is provided so that the inverted pump displacement wave may beviewed by the surgeon during heart augmentation.

As the feedback potentiometer 118 is driven toward ground, it drives theend of withdraw stroke sensor 200. This sensor, modulated by the volumecomparator 201, indicates when the pump has reached the end of thedesired withdraw stroke. The length of stroke is determined by a volumelimit generator described in more detail below with respect to FIG. 8.Sufiice it to state at this point that a signal representative of thedesired volume is carried in line 203. The end of withdraw stroke sensor200 and the volume comparator 201 may consist of an inverting PNPamplifier which drives one-half of an NPN differential amplifier. Theother side of this comparator is driven by the signal representing thedesired volume in line 203 so that a suitable switch (not shown) isturned on whenever the displacement wave amplitude from thepotentiometer 118 exceeds the volume amplitude in line 203. This switchdrives an end of withdrawal oscilloscope output 205 as well as the pumptrigger AND gate 146 and an end of withdraw one shot multivibrator 207for purposes described in more detail below. Line 151 is then energizedand awaits a new pump triggering signal from the blanking gate 144 toinitiate another pumping cycle as described above. In this manner thevolume of blood pumped by the reciprocating pump may be accuratelycontrolled and selected by the surgeon as desired.

During the withdraw stroke, the feedback potentiometer 118 also drives ablanking threshold sensor 210 which provides one of two inputs to ANDgate 141 preventing triggering pulses occurring earlier than apredetermined time before the completion of the withdraw stroke. Thisportion of the circuit is usually only operative during arterio-arterialassist when the EKG trigger level selector 125 is operative. Theblanking threshold sensor 210 may be identical to the end of withdrawsensor 200 except that the input volume signal in line 203 is divided bya ratio of .9 in a volume comparator to 211. The output of the volumecomparator to 211 which occurs a predetermined time before the end ofthe Withdrawal stroke enables AND gate 141. Upon receipt of therefractory gate output signal AND gate 141 enables in turn the AND gate146 through the normally inactive blanking gate 144.

Rate and volume computer circuitry The purpose of the rate and volumecomputer circuitry shown in FIGS. 7, 8 and 9 is, generally speaking, tovary the pump and withdraw rates in response to changes in thetriggering signal rate from the pacemaker 132 selected by the surgeon,and to vary the pump and withdraw rates in response to the desiredvolume per cycle selected by the surgeon. Thus, during completecardiopulmonary bypass, the surgeon need only select the desiredrepetition rate for the pumping cycles by adjusting control 132a on thepacemaker and the computer circuitry will automatically vary the speedof the pumping piston so that the duration of each pumping cyclecoincides with the period of the signal from pacemaker 132. Further, inresponse to the selection of a certain volume per cycle by the surgeon,the computer circuitry varies the length of stroke of piston 15 andautomatically corrects the speed or rate of stroke of the piston so thatthe pump cycle duration remains constant with that determined by theperiod of the signal from pacemaker 132.

When used in arterio-arterial assist, the rate and volume computercircuitry is used to vary the pump and withdraw rates and the volumepumped in response to varying heart cycle times and also in response todilferent desired volumes selected. Further, the output volume pumpeddecreases as a function of the heart rate as the maximum withdrawal andpumping rates are reached.

These maximum rates are determined by blood hemolysis and catheter size.The push and withdrawal rates for each cycle are determined from theheart rate computed on the previous cycle. To eliminate any stackingerrors, a closed loop error detection circuit is provided at the end ofthe withdraw stroke.

The computer logic described briefly above is based upon the selectedrate of pacemaker 132 (or the cardiac cycle time during postoperativeassist) and the selected volume per stroke as variable input parameters.From these the pump and withdraw rates are computed and the pumpcontrolled.

During arterio-aiterial assist it is sometimes more desirable todetermine the cardiac cycle time from a pres sure Wave which is sensedfrom the patient. False triggering of the counting circuitry can beeliminated to a great extent by counting the time interval between thepatients pressure waveforms rather than his EKG wave.

Referring to FIG. 7 wherein the digital counting circuit is shown inschematic form, a pacemaker input signal is received in line 266 frompacemaker 132. With switch 255 connecting line 266 to one shotmultivibrator 271 the digital counting circuitry counts each period ofthe pacemaker pulses and provides an output voltage to the modulationcircuitry shown in FIG. 8 which in turn computes the proper speed of thepumping piston 15. Thus, during complete cardiopulmonary bypass, thedigital counting circuitry shown in FIG. 7 determines the period or rateof the pulses from pacemaker 132.

Alternatively, during arterio-arterial assist the digital countingcircuitry in FIG. 7 may be employed to determine the patients cardiaccycle time as represented either by the patiens EKG wave or a pressuresignal. Toward this end, if switch 131 is placed in its intermediateposition connecting trigger level selector to line 266 the digitalcounter in FIG. 7 will determine the period between the patients R wave.Alternatively, if switch 255 connects the one shot multivibrator 271with line 250a the counting circuit will determine the cardiac cycletime from a pressure input circuit driven by a suitable transducerattached to the patient and impressed on input line 250.

Regardless of the input to the counting circuit, the interval betweensuccessive waveforms is counted by one of the digital counting banks251, channel A, or 252, channel B, and the resulting signal proportionalto the interval between waves or pulses is delivered to the modulationcircuitry in FIG. -8 through output line 250a. The digital countingcircuitry produces a linear output voltage with time as shown in thegraph in FIG. 7.

When the pressure wave is used as an input, it is attenuated by variableattenuator 266a which includes a voltage divider adjustable from asuitable control panel. This waveform drives an AGC circuit 256a whichconsists of dual cascaded field effect transistors. This waveform isimpressed on a pressure trigger level selector 268 which consists of anintegrator, an AC amplifier, an AC signal detector, and a Schmitttrigger. The integrator 267 is provided to prevent the digital counterfrom viewing the portion of the synthesized pressure waveform producedby the pump as a separate triggering wave. The output of the ACamplifier (not shown) is integrated by the integrator 267 and biases theAGC circuitry 256a to maintain a constant amplitude at the AC amplifieroutput. Potentiometer 269 in the pressure trigger level detector 268provides an adjustable bias for the detector so that a selected portionof the patients pressure wave may be employed to initiate the countingcircuitry. With this circuitry, false signals may be filtered andprevented from initiating the digital counting circuit. The Schmitttrigger (not shown) in the pressure trigger level de tector 268 triggersthe one shot multivibrator 271 through selector switch 255. The triggerlevel of the pressure wave may be viewed on the oscilloscope through anisolation oscilloscope driver 272a to output 272. The one shot 11multivibrator 271 generates a 100 microsecond wide pulse.

Of course, the one shot multivibrator 271 may also be triggered by theEKG waveform. It should be remembered that during cardiopulmonary bypassthe one shot multivibrator 271 is triggered only by pulses from thepacemaker 132.

The one shot multivibrator 271 triggers a master flipflop 27212 and aninverter 273. The master flip-flop 272b selects either. channel A orchannel B for counting on alternatively successive cardiac cycles. Themaster flipflop may be a standard dual PNP transistor flip-flop withbase steering. The inverter 273 resets the digital counting banks 251and 252 to erase the count held by the counting banks at the beginningof every other cycle by providing a reset pulse to each of the AND gates274 and 275 upon receipt of each triggering pulse. The master flip-flop27217 provides an enabling pulse to each of the AND gates 274 and 275 onalternate triggering pulses so that after a first triggering pulsechannel A resets and after a second triggering pulse channel B resets.The reset circuits 276 and 277 are conventional transistor switcheswhich reset each appropriate channel by simultaneously base triggeringits associated flip-flops.

The master flip-flop 2721) also enable the AND gates 280 and 281selectively on alternate cardiac cycles, so that the first signal fromthe master flip-flop through line T enables AND gate 280 allowingcounting bank 251 to count, While the second signal from the masterflip-flop 27212 disables the AND gate 280 and enables the AND gate 281through line P so that the flip-flop bank 252 is activated and ready tocount.

The digital pulses for the counting channels A and B are provided by anastable clock 285 which may be a multivibrator or a standard unijunctiontransistor oscillator which triggers a driver flip-flop. When thetrigger pulse from the patients pressure wave energizes the masterflip-flop 27212 which activates one of channels A or B, clock 285delivers digital pulses to it.

Each of the counting banks 251 and 252 consists of a plurality of seriesconnected flip-flops which count pulses from the astable clock 285 inbinary coded fashion. Flipflops 290 to 297 in bank 251 and flip-flops300 to 307 in bank 252 are standard dual PNP transistor flip-flops withbase steering. Each flip-flop divides the frequency of its input signalby 2, successively. Each bank is capable of counting 256 pulses. A threeinput AND gate 309 is provided between the flip-flops 304 and 305 sothat counter circuitry output may not indicate less than a count of 224if it has been inadvertently allowed to exceed a count of 256. Theinputs to the AND gate 309 are driven from the false side of theflip-flops 305 and 306 and 307 so that the trigger pulse to flip-flop305 from 304 is inhibited after each of these three flip-flops has beentriggered once. A similar circuit is provided for bank 251 (channel A).

The false side of each of the counter flip-flops 290 to 297 and 300 to307 may be diode coupled to constant current switches 310 to 317 and 320to 327. Each of the constant current switches is composed of a singlePNP transistor stage which delivers a current flow proportional to itscorresponding count when its associated flipfiop is triggered. Forexample, constant current switch 321 will produce a current proportionalto a count of two, while constant current switch 325 will produce aconstant current proportional to a count of 32 so that the sum total ofthe currents in the constant current switches associated with thetriggered fiipfiops represents the time duration of the cardiac cycle. Acomposite analog readout of the constant current switches is obtained bysumming the currents through a precision resistor 330 associated withchannel A or a precision resistor 331 asociated with channel B. Channelswitches 335 and 336 are single transistor stages which alternativelyshunt the precision 12 output resistors 330 and 331. The channel whichis counting is always shunted by the channel switches which are drivenby master flip-flop 27212 through either line F or T. An added 337receives a constant DC voltage at its input from one or the other ofchannel switches 335 or 336.

As described in more detail below, a timing error sensor circuit isprovided for correcting any error between the actual displacement cycletime and the period of the input signal from the pacemaker, or theactual cardiac cycle time (in arterio-arterial assist). This error, ifit is negative, is delivered to the isolation circuitry output 337athrough line 340 where it subtracts from the counted input signal periodto provide a new effective period. If it is positive it is alsodelivered to the isolation circuitry output 337a where it adds to thecounted period. As the period of the input signal delivered to the oneshot multivibrator 271 is the controlling parameter for the computermodulating circuitry it is possible to correct errors in thedisplacement cycle time by varying the effective period signal to themodulation circuitry through line 252a.

It is apparent that each of the channels 251 and 252 count on alternateinput signals so that upon completion of any one cycle channel A willread out to the modulating circuitry in response to a change in state ofmaster flip-flop 272b, while at the same time channel B counts. Upon theinitiation of the counting circuitry by the next input signal pulsewhich changes the state of master flip-flop 2721: again, channel B readsout to the modulating circuitry and channel A counts.

Referring to FIG. 8 wherein the modulating circuitry for determining thepush and withdrawal rates is schematically shown, a saw toothedoscillator 350 produces a saw tooth waveform as shown at 351 with arising ramp voltage and a very steep retrace. The saw tooth oscillator350 may consist of a unijunction relaxation oscillator driven by aconstant current source. The output may be capacitively coupled to avariable voltage divider which is internally adjusted to compensate forthe voltage gain tolerance of the unijunction oscillator.

A duty cycle modulator 352 is provided for relating the desired orlimited blood displacement volume to a time base. The output of the dutycycle modulator 352 is a pulse having a width modulated proportionallyto the desired or limited volume of blood to be displaced.

A clipping amplifier 353 is provided for setting the maximum volume, andhence the maximum pump and withdraw rates, for given heart cycle period.This circuit is only operative during arterio-arterial assist when thesystem responds to the patients EKG wave. To achieve this, the linearvoltage which represents the heart period is impressed on line 355 andconstitutes an input to the clipping amplifier 353. It will be recalledthat there is a maximum volume which may be pumped or should be pumpedfor every heart cycle period. In this regard, the clipping amplifier 353prevents excessive withdrawal and pump rates caused by an extremely fastheart beat rate counted by the digital counter in FIG. 7. The clippingamplifier 353 may consist of a two stage DC amplifier having an NPNtransistor driving a PNP transistor, with gain quiescent bias adjustmentprovided by the patients computed cardiac cycle time.

A catheter size selector switch 356 is provided for varying the maximumvolume limitation determined by the clipping amplifier 353 for dilferentcatheter sizes.

The relationship of heart rate or pacemaker rate to the maximumpermissible volume may be drawn as exponential curves based upon thetransfer characteristics of each individual catheter size. Therefore,the maximum permissible volume for any catheter size is a complexfunction of the flow characteristics of the particular catheter used.The catheter size selector switch 356 in response to the selection ofany of the catheter sizes biases the clipping amplifier 353 to vary thegain thereof and hence the maximum permissible volume in accordance withcalculated data. An emitter resistor for the PNP stage in the clippingamplifier 353 is selected from one of eight resistors which correspondto eight catheter sizes. Hence, the gain of the clipping amplifier 353is selected by the selector switch 356. In addition an output resistivevoltage divider is connected to the collector of the PNP transistor andone of eight resistors is simultaneously selected to adjust the outputquiescent level of the DC amplifier. By this circuitry the clippingamplifier 353 produces output voltages varying with the heart period, orpacemaker, for each catheter size.

It should be noted that the clipping amplifier 353 merely sets themaximum limit of the volume pumped during any cycle and that for anylesser volume selected by the surgeon will normally determine the pushand withdrawal rates.

A volume limit generator 358 biases the duty cycle modulator 352 toachieve a pulse output from the duty cycle modulator having a widthproportional to either the maximum permissible volume or the manualvolume selected, if it is less than the maximum permissible volume whichis determined by the clipping amplifier 353.

The duty cycle modulator 352 may consist of a twotransistor stage DCamplifier, followed by a regenerative switch and an NPN resettransistor. The sawtooth oscillator output is amplified and provides aforward bias to the first stage of the regenerative switch.Simultaneously, a back bias is provided by the volume generatorcircuitry. When the sawtooth amplitude exceeds the volume amplitude, theregenerative switch turns on. When the sawtooth waveform retraces tostart another ramp, the NPN reset transistor turns on, resetting theregenerative switch to its normally off condition. The DC amplifier gainis manually adjustable to accurately match the volume generator output.

A manual volume adjust 360 is provided which normally controls the levelof the bias of the volume limit generator on the duty cycle modulator352. Therefore, the width of the pulse from the duty cycle modulator 352is normally proportional to the manually adjusted volume unless themaximum volume limit for a particular heart rate is exceeded. The outputof the clipping amplifier 353, which is discussed above, is a signalproportional to the maximum permissible volume and hence the maximumpermissible pump and withdraw rates. It drives an emitter follower inthe volume limit generator 358' which limits the output of the volumeadjust potentiometer in the manual volume adjust 360 to a valueproportional to the maximum permissible volume. The emitter of theemitter follower is diode coupled to the wiper of the volume adjustpotentiometer and hence the low driving point impedance of the emitterfollower effectively modulates the relatively high impedance of thecircuit associated with the volume potentiometer. The volume adjustpotentiometer is connected in series with a voltage divider wherein itswiper is the output of the volume limit generator 358. The potentiometerin the manual volume adjust 360 may be on the control panel so that thesurgeon may select the desired volume.

A catheter select switch 363 is provided which selects either one or twocatheters. The catheter select switch 363 selects the range of thevoltage divider in the volume limit generator 358. Switch 363 dividesthe bias to the PNP limiting emitter follower from 2:1. Thus, catheterassembly 49 shown in FIG. 1 may consist of either one or two catheters.When one catheter is used instead of two, the catheter select switch 363approximately halves the maximum permissible volume limit, whichcontrols or limits the output of the volume adjust potentiometer 360.When two catheters are used, the two catheter switch in the catheterselect switch 363 approximately doubles the maximum voltage the voltageadjust potentiometer 360 may produce over the single catheter selectswitch position. It should be noted again that the catheter selectswitch 363,

the catheter size selector switch 356 and the clipping amplifier 353limit only the maximum volume which may be pumped without exceeding themaximum withdrawal and pump rates. They do not affect the width of theoutput pulse from the duty cycle modulator 352 unless the potentiometerin the manual volume adjust circuit 360 attempts to produce a voltagerepresenting a volume which would produce excessive rates.

The volume limit generator 358 drives an output line 203 for deliveringa signal representing the desired volume to: (l) a volume indicator (notshown) for visual representation, (2) to the withdrawal volumecomparator 201 which enables the pump trigger AND gate 146 as describedabove with respect to FIG. 6, and (3) to the blanking volume comparator211 which enables the AND gate 141 which transfers the delayed pumptriggering signal to I blanking gate 144.

The above circuitry produces a pulse width modulated pulse train fromthe duty cycle modulator 352 proportional to the desired volume of bloodto be pumped. As the heart rate varies or the pacemaker rate is variedby the surgeon, it is apparent that the withdrawal or the pump rate mustchange to maintain the same volume of blood delivered and to achieve atime coincidence between the displacement cycle and the period of thepacemaker signal (or the cardiac cycle). For this purpose, an amplitudemodulator 370 and a gain break amplifier 371 are provided for amplitudemodulating the pulse train from the duty cycle modulator 352. The inputto the gain break amplifier 37-1 (line 355) is a voltage proportional tothe period of the pacemaker signal (or the heart cycle) determined bythe digital counter in FIG. 7. The voltage in line 355 is linear withrespect to time. Since the Withdrawal and pump rates must beproportional to the frequency of the pacemaker signal or the patientsheart, linear voltage at 355 must be converted to an exponential voltagerepresenting frequency. Hence, the patients heart period or pacemakerperiod which is on a time base must be converted to a frequency base sothat the amplitude modulator 370 produces a pulse train having anamplitude proportional to the frequency of the heart signal or pacemakersignal.

For this purpose the gain break amplifier 371 produces an exponentialoutput voltage as shown in graph 375 in response to a linear voltageinput from line 355. The gain break amplifier 371 consists of an emitterfollower which drives a voltage divider. The impedance of the voltagedivider is a function of the divider output voltage. As the voltageincreases diodes in the circuit become for ward biased, couplingsuccessive resistive loads to the output. There are six of these gainbreaks which generate an exponential output curve from the linear inputvoltage at line 355. The gain break output is amplified by a single NPNstage which modulates the amplitude modulator. Since heart frequency isan exponential reciprocal function of the heart period or pacemakerperiod, the gain break amplifier 371 effectively provides an exponentialvoltage output proportional to the frequency of the pacemaker signal orcardiac cycle.

The amplitude modulator 370 may consist of a single PNP transistorinverting amplifier driven by the pulse width modulator pulse train fromthe duty cycle modulator 352. The emitter of this PNP inverter amplifierin the amplitude modulator 370 is back biased by the output of the gainbreak amplifier 371. The net collector current flow in the amplitudemodulator 370 is therefore directly proportional to the differential ofthese two biases. In this manner the pulse train output from theamplitude modulator 370 has an amplitude proportional to the frequencyof the pacemaker signal or cardiac cycle.

An integrating amplifier 377 is provided for integrating the pulse trainwhich is modulated both with volume and with pacemaker frequency. Theintegrating amplifier 377 is a conventional RC integrator which drivestwo NPN DC amplifiers in parallel. The integrating amplifier 377produces a DC analog voltage equal to the duty cycle times the peakoutput voltage which is actually proportional to the desired volumetimes the pacemaker frequency. Therefore, the DC voltage output has alevel proportional to the desired pump and withdraw rates. It isapparent that as the frequency of the pacemaker increases, as computedby the gain break amplifier 371, the pulse amplitude from the amplitudemodulator 370 will increase as will the DC level from the integratingamplifier 377. Therefore, as the pacemaker frequency increases, so dothe push and withdraw rates to achieve coincidence between the pacemakersignal period and the displacement cycle. Similarly, as the desiredvolume increases, represented by the output voltage from the volumelimit generator the pulses from the duty cycle modulator 352 willincrease also producing an increase in the DC level voltage output fromthe integrating amplifier 377 resulting in an increase in pump andwithdrawal rates.

The DC voltage output from the integrating amplifier 377 biases a chargegate 378 and a discharge gate 379. The gates 378 and 379 may eachconsist of an NPN transistor, the collector of which modulates a pair ofPNP transistor drivers. The PNP transistors are forward biased, inparallel, by the integrating amplifier. If the NPN gating transistor isturned on, both PNP transistors are back biased. It will be recalledthat during the withdraw stroke, line 152 is energized by theregenerative switch 148 and during the pump phase line 151 is energizedby the regenerative switch. During the withdrawal phase, line 151 turnson the NPN gating transistor in the discharge gate 379 back biasing thePNP transistors in the discharge gate 379. The absence of a signal online 152 produces an output to charge driver 381 and line 382 whichenergizes the withdraw phase driver 188 as shown in FIG. 6. The withdrawphase then proceeds at a rate corresponding to the magnitude of thecurrent in line 382.

When the regenerative switch 148 deenergizes line 151 and energizes line152, the charge gate 378 turns on ending the withdrawal stroke and thedischarge gate 379 turns oif initiating the pump stroke by energizingthe push phase driver through line 160. The pump stroke rate isdetermined by the integrating amplifier 377 similar to the withdrawstroke. A charge driver 381 is associated with the charge gate 378 inthe same manner as the discharge driver 383 is driven by the dischargegate 379.

A closed loop error feedback circuit is provided for achievingcoincidence between the reference waveform produced by the modulatingcircuitry in FIG. 8 and the actual displacement waveform produced by thefeedback potentiometer 118. Referring to FIG. 8, the charge driver 381and the discharge driver 383 drive a reference ramp generator 385. Theramp generator 385 may be a low leakage wet tantalytic capacitor with aminimum voltage clamping circuit. The clamping circuit may be a resistorvoltage divider which is diode coupled to the reference capacitor. Thereference ramp generator 385 produces a triangular waveform proportionalto the desired displacement of the reciprocating heart pump piston withrespect to time. Thus, the reference ramp generator produces a referencesignal which biases one side of a comparator 386. The sense of thereference signal is determined by the regenerative switch 148.

The comparator 386 may be simple NPN transistor comparator forwardbiased by the reference ramp generator 385. The back bias for thistransistor is provided by the feedback voltage from the potentiometer118 which is inverted by the inverting amplifier 170 shown in FIG. 6. Itis amplified by a two stage, non-inverting DC amplifier 388, shown inFIG. 8. As long as the reference ramp waveform from the referencegenerator 385 coincides with the inverted displacement waveform from theamplifier 388, a fixed quiescent voltage drives both the low erroramplifier 389 and high error amplifier 390. The low error amplifier 389may consist of a dual PNP inverter which drives a resistive voltagedivider, and amplifies the negative error voltage between the referenceand displacement wave voltages. The high error amplifier 390 may consistof a PNP transistor stage which drives a resistor voltage divider, andamplifies the positive error between the reference and displacement wavevoltages. The outputs of the low error amplifier 389 and the high erroramplifier 390 are connected to their associated AC amplifiers, 173 and190, respectively, through AND gates 395 and 396.

The AND gates 395 and 396 along with an associated chopper flip-flop 398provide continuous repetitive error correction during the withdraw andpump phases. The chopper flip-flop 398 is driven by the sawtoothoscillator 350 through line 400 and provides alternate enabling pulsesto AND gates 395 and 396 through'switches 402 and 403, respectievly. Itis apparent that if the sawtooth oscillator provides sawtooth pulses onthe order of microseconds that AND gates 395 and 396 will be enabledmany times during each pumping cycle and therefore provide a virtuallycontinuous error correction of the pump and withdraw rates. The pump andwithdraw rates determine the volume delivered.

As discussed above, the push and withdraw rates for each cycle aredetermined by the modulating circuitry of FIG. 8 from the pacemaker ratecounted in the previous period of the pacemaker signal by the digitalcounter described in FIG. 7.

Referring now to FIG. 9, a timing error sensor circuit generallydesignated by the numeral 415 is provided for computing the timedifference between the completion of the withdrawal stroke and thereceipt of a pump cycle trigger signal. The resulting error signal isused to vary the pump and withdrawal rates during the next cycle inclosed looped fashion. This closed loop approach to error correctioncompensates for actuator gain variations and counting errors. The timingerror sensors 415 are essentially two channels which integrate the errordefined by the on time of a regenerative switch which is a pulseproportional to the time error between the end of withdraw stroke andthe pump triggering signal. Channel 416 determines the error when thepumping cycle is completed before the next triggering pulse is receivedby the blank gate 144, and channel 417 determines the error when thepump triggering signal from the blanking rate is received before the endof the cycle. Therefore, channel 416 determines the error when the pumpand withdraw rates are too fast for a particular pacemaker period andchannel 417 determines the error when the pump and withdrawal rates aretoo slow for a particular pacemaker period (or cardiac cycle).

Each of the timing error sensor channels 416 and 417 are substantiallyidentical except for having cross connected inputs. Differentiators 418and 419 receive input pulses respectively from the end of withdrawstroke one shot multivibrator 207 and the blanking gate 144. Thedifierentiators 418 and 419 may be typical RC type. The differentiatedinput signal from the ditferentiators 418 and 419 turn on regenerativeswitches 421 and 422 The regenerative switches 421 and 422 may each bestandard two PNP transistor cascaded switches with the output fed backto the input. Reset stages 424 and 425 are provided for turning offtheir respective regenerative switches 421 and 422. The input to thereset stage 424 is the blanking gate output v144, while the input to thereset stage 425 is the end of withdraw multivibrator 207. The resetstages 424 and 425 may each be diode coupled resistor logic which biasesthe regenerative switch off upon receipt of the appropriate logiccommand. The time duration that each of the regenerative switches 421and 422 are on represents the positive or negative error between thepumping cycle and the period of the pacemaker signal (or patientscardiac cycle). The regenerative switches 421 and 422 drive integratingamplifiers 428 and 431 which produce a DC voltage proportional to thepulse time duration of their associated regenerative switch outputs. Theintegrating amplifier 428 and 431 may each consist of a two stagetransistor switch, followed by an RC integrator and a single NPNtransistor DC amplifier. The output pulse of integrating amplifier 428drives a readout amplifier 429. The readout amplifier 529 may consist ofa PNP transistor DC amplifier. Channel 417 has a similar NPN transistorreadout amplifier 432.

If the displacement cycle is too fast compared with the pacemaker periodor cardiac cycle, the end of withdraw stroke multivibrator 207 will turnon regenerative switch 421 before an output pulse from the blanking gate144 initiates the reset stage 424 producing a DC error output fromreadout amplifier 429. The error signal from the readout amplifer 429increases the current in the isolation circuit summing resistor in thedigital counting circuit shown in FIG. 7. Since this current representsthe time period of the pacemaker 'wave or cardiac cycle, the readoutamplifier 429 effectively lengthens the counted pacemaker cycle orcardiac cycle time, producing a new, effective cycle time. Since thecycle time has been effectively increased, the modulating circuitry,shown in FIG. 8, views an effectively longer cycle time than it wouldview without the addition of the error signal. Since an increase in thepacemaker or cardiac cycle count produces a reduction in the withdrawaland push rates determined by the modulating circuitry in FIG. 8, thedisplacement wave slows down on the next pump cycle to correct for thiserror. Conversely, if the pump cycle is too slow compared with thepacemaker or cardiac cycle, a triggering pulse from the blanking gate.144 will turn the regenerative switch 422 on before the end of withdrawstroke multivibrator 207 resets the regenerative switch 422 so thatreadout amplifier 432 produces an output voltage proportional to thetime error. This error signal decreases the current in the isolationcircuit summing resistor in the'counting circuitry shown in FIG. 7, toeffectively reduce the counted pacemaker or cardiac cycle time computedby the digital counter circuit. The modulating circuitry shown in FIG. 8will View a reduced cycle time and will increase the pump and withdrawalrates on the next pump cycle to correct for this error.

During arterior-arterial assist, the pump triggering pulse occurs veryearly in the cardiac cycle, i.e., a predetermined time before the end ofthe withdrawal stroke as determined by the blanking threshold sensor 210and the volume comparator 211, the AND gate 141 will drop the triggeringsignal so that there is no output from the blanking gate 144 andtherefore no error output from the channel 417 timing error sensor whichnormally indicates that the pumping cycle is too slow. In this case, thepump and withdrawal rates are determined by the cardiac cycle timecounted by the digital counting circuit on the previous cardiac cyclewithout the modulation of any error fromthe timing error sensors.

Single stroke initiation The present device is provided with means forinitiating a single pump stroke. The purpose of providing thiscapability is to enable the system to be used for injecting radio-opaquedies in the cardio vascular system and/or to obtain coronary angiograms.Referring to FIG. 6, when the select switch 131 is placed in its manualposition a suitable circuit is provided for withdrawing the actuatingshaft to the end of the withdraw stroke. In this mode the triggeringpulses from the EKG trigger selector 125 and the pacemaker 132 aredisconnected from the control system so that repetitive pumping actionis prevented. Upon the closure of the spring loaded manual strokeinitiate switch 133 lockout gate 450 disables the blanking gate 144.This prevents the initiation of a triggering pulse from AND gate 141. Atthe same time, a withdraw disable gate 452 is activtaed which disablesthe withdraw driver 194 and prevents any initiation of the withdrawstroke. Actuation of switch 133 also energizes line 453 chargingcapacitor 454 which initiates a pump triggering signal to line 150turning the regenerative switch 148 on energizing line 151 and therebyinitiating a single pump stroke of the reciprocat- Reduced augmentationcircuit Referring to FIG. 10, a reduced augmentation circuit 460 isprovided for skipping one or three cardiac cycles. In this manner theheart pump system will operate only on selected pacemaker pulses orselected beats of the patients heart, if desired. A disable gate 461 isprovided for disabling the blanking gate 144 except when selectedtriggering pulses are received by blanking gate 144. A switch 462 isprovided for selecting one hundred percent augmentation, fifty percentaugmentation and twenty-five percent augmentation as shown. With theswitch in the one hundred percent augmentation position, the disablegate 461 completely disables the blanking gate 144 and permits alltriggering pulses from the AND gate 141 to be coupled to AND gate 146.In this event all normal triggering pulses from refractory gate initiatea pump cycle on each pacemaker pulse or cardiac cycle. When switch 462is in the fifty percent augmentation position, a flip-flop 463 enablesthe disable gate 461 to blank alternate triggering signals from AND gate141 and effect a pump cycle only on alternate pacemaker pulses orcardiac cycles. Flip-flop 463 is tripped to either state by refractorygate 140. This is important because if reduced augmentation wereresponsive to a time type blanking gate, an increase in the heart ratemay produce the blanking gate, an increase in the heart rate may producethe blanking of more than one triggering pulse even if fifty percentaugmentation was desired. Another flip-flop 464 cascaded with flip-flop463, and an AND gate 465 are provided to drive the twenty-five percentaugmentation. Now on every fourth beat of the patients heart (or pulsefrom the pacemaker 132) the binary flip-flop 464 which is the fourthbinary stage activates AND gate 465 and the disabled gate 461 permittinga pulse to pass through the blanking gate 144. In this manner threecardiac cycles or pacemaker pulses may be skipped regardless ofvariations in the repetition rate of the input signal to the system.

Power supply Referring to FIG. 11, a two contact switch 490 is providedconnected to a 30 volt DC power supply. When switch 490 is in its upperposition, a release coil 491 is energized deactivating the singlecatheter select switch 492 and a dual catheter select switch 493. Thisassures that each of the catheter select switches will be placed intheir olf positions when the system is turned on assuring the correctcatheter selection on the next use of the pumping system. When switch490 is placxed in the lower position, i.e., the on position, releasecoil 491 is deenergized permitting the manual selection of either thesingle or dual catheter switches 492 and 493. At this time the coil 495is energized connecting the hydraulic power supply to a source ofelectric power. At the same time, the electric control circuitry isenergized with the exception of the pump and withdraw servo coils 147and 154 respectively.

Before pump and Withdraw servo coils 1-47 and 154 may be energized, itis necessary that the surgeon perform the following functions; (1)select either the single or the dual catheter switches 492 or 493, (2)choose a catheter size by actuating the catheter size selection switchwhich energizes a holding coil 497, (3) and set the manual volume adjustpotentiometer 360 to zero volume which by suitable circuitry closesswitch 498. After the surgeon has made all these selections, relay 499may be energized by closing switch 503 so that contacts 2 and 3 aremade, placing the circuit in the operate position indicated by theenergization of an operate lamp 501 on the control panel. If the surgeonhas failed to make one of the parameter selections, no current will fiowthrough the coil 499 and even if the surgeon actuates the start switch503, power will not be supplied to the pump and withdraw servo coils 147and 154. In this case, coil 499 will not be energized and contacts 4 and1 of relay 500 will be closed lighting a standby lamp 504 on the controlpanel indicating to the surgeon that he has failed to make a parameterselection. A lamp 506 is also provided on the control panel forindicating when the catheter size select switch 363 has been closed.

The operation With the components and catheters connected and arrangedaccording to FIGS. 1 and 2, or alternatively according to FIGS. 4 or 5,the power supply circuit shown in FIG. 11 is placed in the standbyposition. The surgeon then makes the various catheter selections andadjusts the volume potentiometer to place the power supply circuit inthe operate position indicated by the operate lamp 501. The piston 15 atthis time is at the end of the pump stroke. The various oscilloscopeoutlets are connected so that the surgeon views the various parametersand the start switch 503 is tripped preparing the control circuitry forthe receipt of a pump triggering signal. Switch 131 is placed in thepacemaker position and switch 255 is moved to a position connecting line266 with the one shot multivibrator 271. The surgeon then adjusts thepacemaker 132 to the desired repetition rate of the pumping cycles.

The delay one shot 136 may be adjusted so that the output pulses to therefractory gate are in phase with the pulses from the pacemaker 132 asno delay time is necessary in complete cardiopulmonary bypass.

Pulses from the refractory gate 140 trigger the regenerative switch 148and the pump proceeds through its pump stroke forcing blood into thepatients arterial tree through catheter assembly 49. Then the piston 15proceeds through a stroke dictated by the volume potentiometer 360associated with the volume limit generator 358, the regenerative switch148 is turned off reversing the piston 15 causing blood to be drawn fromreservoir 36 into pump chamber 16. This cycle is repeated w1th eachtriggering pulse from the pacemaker 132.

If the surgeon desires to increase the arterial flow rate, the frequencyor repetition rate of the pacemaker 132 may be increased. In response toan increase in the rate of pulses from pacemaker 132, the modulatingcircuitry shown in FIG. 8 will increase the speed of stroking of piston15 so that the pump cycle corresponds with the newly selected period ofthe pacemaker signal. Further, the arterial flow rate may also beincreased by increasing the selected volume on the manual volume adjust360. In response to this change the volume comparator 201 (controlled bythe volume limit generator 358) increases the length of stroke of thepiston 15, and the duty cycle modulator 352 at the same time increasesthe speed of stroke of the piston 15 so that the newly selected volumeper cycle will be achieved without variation in the time duration of thepumping cycle.

The proper operation of the present system in complete cardiopulmonarybypass depends upon the proper balance of the manually controlledparameters of volume per stroke and pacemaker rate. If the pacemakerrate is too high, the speed of stroking of the piston 15 will produceblood damage. If the pacemaker rate is too slow, the selected volume perstroke must be increased and this may rupture the small vessels. Thus,the volume adjust ment and rate control must be varied to obtain optimumphysiological results between these two limits.

As noted above, the present system may be used postoperatively as anarterio-arterial circulation assist after complete cardiopulmonarybypass. T 0 place the system in this mode it is merely necessity toclose valve 11 and connected the various inputs to the computing andtriggering circuitry so that the patients EKG wave triggers the pumpingcycles. The phasing in this mode is described in detail in our abovementioned copending application.

Thus far, tests on animals have indicated no tendency toward metabolicacidosis with the present complete cardipulmonary bypass system evenafter extended perfusion. With one exemplary test animal completecardiopulmonary bypass proceeded as follows. The dog was not allowed tocool, but to warm slowly from 37 degrees centigrade to 39.5 degreescentigrade for one hour, then allowed to cool to 34 degrees centigradeover 45 minutes, and then warm to a normal 37 degrees over the next 30minutes, the latter temperature being maintained for a further 30minutes.

At the beginning of the perfusion the peak flow rate was 1,720 ccs. perminute or 62 ccs./kg./min. i.e., peak flow per pump cycle. The flowrates used herein are the peak flow rates attained at the top of theflow curves, the actual flow per cycle being much lower. A pulsed-fieldelectromagnetic flow probe was placed around the common iliac artery,from which the adventitia had been stripped to avoid interference withthe readings, for the purpose of sensing the blood flow rate in theanimal. It was placed far enough away from the pump catheter so thatvariations in its diameter with the withdrawal and pump stroke would notaffect the electrical fit for the flow probe.

The pressures attained at the initial flow rate were 150/100 whichappeared adequate. After 45 minutes the flow rate was readjusted to1,380 ccs. per minute peak flow, or 49.5 ccs./kg./min. peak flow percycle. Pressure was then an acceptable /70. Only 350 ccs. of saline wereadded during the first hour and this was less than the loss. Theperfusion continued for 3 hrs. The animal was acidotic (respiratory) atthe outset of the perfusion with arterial pH being 7.18 and the venouspH being 7.15. After two hours of pulsatile perfusion the arterial pHhad risen. Both the arterial and venous pHs increased toward normalduring the third hour of perfusion. There was no tendency towardmetabolic acidosis. The arterial and venous carbon dioxide contents andthe pCO levels all declined during the third hour of perfusion. Thelactate pyruvate levels rose, but the lactate pyruvate ratios remainedstationary or declined slightly during the perfusion. Thus, theperfusion of the arterial tree seemed adequate enough to prevent poolingof blood with resultant tissue hypoxia. Similar biochemical results werefound in the other animals.

We claim:

1. A heart pump system for complete cardio-pulmonary bypass, comprising:a pulsatile pump having a pumping chamber, a piston reciprocable withinsaid pumping chamber having push and withdraw phases defining a pumpingcycle, catheter means for receiving blood from the venous side of apatients circulatory system, oxygenator means connected to receive andoxygenate blood from said catheter means, means for conveying blood fromsaid oxygenator means to said pumping chamber, second catheter meansconnecting said pumping chamber with the arterial side of the patientscirculating system, means for reciprocating said piston so thatoxygenated blood flows into the patients circulatory system in pulsatilefashion; and control means for said reciprocating means including meansfor deriving pump triggering signals corresponding with the desiredrepetition rate of the pumping cycle, means for initiating the pumpingcycles in timed relationship with said pump triggering signals, manuallycontrolled means for varying the volume of blood pumped on each pumpingcycle, and means responsive to said manually controlled means forautomatically increasing the blood flow rate through said secondcatheter means as the selected volume of blood is increased, saidmanually controlled means including means for varying the length ofstroke of said piston, said means for automatically increasing the bloodflow rate including means for increasing the rate of movement of saidpumping piston.

2. A heart pump system for complete cardio-pulmonary bypass, comprising:a pulsatile pump having a pumping chamber, a piston reciprocable withinsaid pumping chamber having push and withdraw phases defining a pumpingcycle, catheter means for receiving blood from the venous side of apatients circulatory system, oxygenator means connected to receive andoxygenate blood from said catheter means, means for conveying blood fromsaid oxygenator means to said pumping chamber, second catheter meansconnecting said pumping chamber with the arterial side of the patientscirculating system, means for reciprocating said piston so thatoxygenated blood flows into the patients circulatory system in pulsatilefashion; and control means for said reciprocating means including meansfor deriving pump triggering signals corresponding with the desiredrepetition rate of the pumping cycle, means for initiating the pumpingcycles in timed relationship with said pump triggering signals, manuallycontrolled means for varying the volume of blood pumped on each pumpingcycle, and means responsive to said manually controlled means forautomatically increasing the blood flow rate through said secondcatheter means as the selected volume of blood is increased; and meansfor preselecting the repetition rate of said triggering signals asdesired, said manually controlled means including computer meansresponsive to the period of said triggering signals for providingsubstantial coincidence between said triggering signal period and saidpumping cycle, said computer means being reponsive to a change in theselected volume for varying the speed of said piston to achieve saidcoincidence, whereby the speed of said piston will increase and decreasewith the selected blood volume.

3. A heart pump system for complete cardio-pulmonary bypass, comprising:a pulsatile pump having a pumping chamber, a piston reciprocable withinsaid pumping chamber having push and Withdraw phases defining a pumpingcycle, catheter means for receiving blood from the venous side of apatients circulatory system, oxygenator means connected to receive andoxygenate blood from said catheter means, means for conveying blood fromsaid oxygenator means to said pumping chamber, second catheter meansconnecting said pumping chamber with the arterial side of the patientscirculating system, wherein said second catheter means permitting bloodflow in either direction, said second catheter means and said conveyingmeans having a relative resistance to flow such that during the withdrawstroke of said piston a substantial portion of the blood will bewithdrawn from said conveying means rather than from said secondcatheter means, means for reciprocating said piston so that oxygenatedblood flows into the patients circulatory system in pulsatile fashion;and control means for said reciprocating means including means forderiving pump triggering signals corresponding with the desiredrepetition rate of the pumping cycle, means for initiating the pumpingcycles in timed relationship with said pump triggering signals, manuallycontrolled means for varying the volume of blood pumped on each pumpingcycle, and means responsive to said manually controlled means forautomatically increasing the blood flow rate through said secondcatheter means as the selected volume of blood is increased.

4. A heart pump system for cardiopulmonary bypass and postoperativearterio-arterial assist, comprising: a pulsatile pump having areciprocating piston the push and withdraw strokes of which define apumping cycle, said piston defining a fluid chamber in said pump, meansfor receiving and modifying a signal representing one of the patientsphysiological parameters and producing pump cycle triggering signals forcirculatory assist, pacemaker means for deriving pump cycle triggeringsignals for bypass operation, control means for initiating each pumpingcycle, selectively operable means for connecting the output of saidproducing means or said deriving means to said control means, cathetermeans connecting said fluid chamber into the patients circulatory systemso that fluid is delivered thereto during the push stroke of saidpiston, means for conveying fluid into said fluid chamber during bypassoperation, said conveying means having a check valve for preventing theflow of fluid from the fluid chamber into the conveying'means, saidcatheter means being unrestricted so that fluid may flow in eitherdirection therethrough during arterio-arterial assist, and valve meansfor closing said conveying means during arterio-arterial assist.

5. A heart pump system as defined in claim 4, wherein said check valveis mounted within said valve means.

References Cited UNITED STATES PATENTS 2,847,008 8/ 1958 Taylor et al23258.5 2,927,582 3/1960 Berkman et al. 23258.5 3,099,260 7/1963Birtwell 1281 3,183,908 5/1965 Collins et a1. 23258.5 3,266,487 8/ 196 6Watkins et a1. 1281 OTHER REFERENCES Murphy: Trans. Amer. Soc.Artificial Inter. Organs, 1961, vol. VII, pp. 361-68.

DALTON L. TRULUCK, Primary Examiner US. Cl. X.R. 23-25 8.5

